With the ever-increasing number of amputees needing prosthetic devices, various types of foot and leg prostheses have been developed. In the past, prosthetic devices usually comprised of some form of artificial limb or rod extending to the ground merely to support body weight. More recently, other devices have been made to imitate the structure of the human foot and leg, as well as to simulate their natural movement. Many consisted of a hinge to allow movement between the leg and foot.
The gross inadequacies of these type of devices became readily apparent as they tended to be bulky, heavy, non-resilient, and provided little or no energy absorption, storage and release. As such, the amputee's activity level was severely limited. As a result, it was unheard of for amputees to participate in sporting activities such as tennis, basketball, jogging and skiing.
Various improvements to prosthetic devices have enabled the amputee to substantially increase his or her activity level. A prosthetic foot and leg device which allows a high degree of mobility on the part of an amputee was disclosed in my U.S. Pat. No. 4,457,913 entitled "Composite Prosthetic Foot and Leg." That patent disclosed a prosthetic foot and leg device utilizing a resin impregnated high strength filament structure for the leg portion, foot portion and heel portion, with all three regions being provided with substantial elastic flexibility, of relatively low energy absorption characteristics, so as to give the wearer high mobility with a relatively natural feel. Additional improvements have been made to prosthetic devices to greatly enhance the lifelike movement of the foot, and to improve the adjustability and interchangeability of the devices to custom fit various amputee weights, gaits, activity levels and other conditions unique to the individual amputee.
Such improvements are also disclosed in U.S. Pat. Nos. 4,822,363 entitled "Modular Composite Prosthetic Foot and Leg," and 5,037,444 entitled "Prosthetic Foot." In each of these patents, a substantially low energy absorbing material, utilizing a resin impregnated high strength laminate, is used in conjunction with a substantially low energy absorbing structure, comprising elongated curvilinear sections, extending from the stump of the amputee down and forward, with a heel portion extending rearward. This combination of material and structure greatly improves the wearability of the prosthetic device, and has enabled the amputee to resume substantially normal activities.
In the past, attempts have been made to utilize air cushions in various prosthetic devices, but none were designed to enhance activity levels beyond the expected sedentary levels of most amputees. In particular, none of the prior devices improved the dynamic performance of the prosthesis through the entire roll-over motion of a normal gait, i.e., the transfer of weight and motion from the initial heel strike to toe-off.
Generally, persons walk or run by transferring weight from the heel to the toe during a normal gait, with the weight being transferred from the initial heel strike, to the mid-stance, to the toe-load, and then to the toe-off. The heel-strike represents the initial contact between the heel and the ground, the mid-stance represents the period where weight is distributed over the foot, the toe-load represents the period where weight is on the front end of the foot, and toe-off represents the period immediately after pushing off. In addition, this heel-to-toe movement is constantly monitored by the person's proprioception, which helps the individual constantly adjust his or her balance, without which he or she would be prone to become off-balance.
U.S. Pat. No. 2,197,093 to Campbell discloses an air cushion located on the sole of an artificial limb to provide a pneumatic cushion arrangement for artificial feet. This structure, however, did not accommodate the normal heel-to-toe transfer of weight, from the heel strike to the toe-off. For instance, at the moment of heel strike, as the heel portion of the cushion is compressed, the air in the cushion is likely to be forced forward from the heel to the toe end. Thus, at the heel strike, the point of greatest impact, the air cushion would tend to flatten as it is compressed, and would not provide adequate support. Also, if attempts were made to cure the migration of air by inflating the cushion to a substantially high pressure, the air cushion would lose its ability to absorb and store energy, and would become too stiff to provide a smooth roll-over from heel to toe.
Therefore, there is a need for a prosthetic device having an air bladder system which addresses the entire spectrum of an amputee's normal stride.